1. Field of the Invention
This invention relates to gas-fired water heaters, and more particularly to such water heaters of the kind in which heat exchange takes place by direct contact of the combustion product gases from a gas burner with the feed water.
2. The Prior Art
One known heater of this kind uses a low intensity ring-type gas burner, the combustion products of which flow up and down through annuli in the heater and come into direct contact with high pressure jets of feed water. The disadvantages with this type of heater is that it is both bulky and costly in that it uses a large low-intensity burner system, large and complicated heat transfer members, and a complicated high pressure sprayed water pumping system whose range of water flow rates is small.
Another known heater of this kind uses a burner which fires horizontally into an open-bottomed combustion canopy located in the path of downwardly flowing feed water droplets, the combustion product gases emerging from the bottom of the combustion canopy and flowing upwardly in direct contact with the water droplets. This kind of water heater relies upon a large upper surface area for the combustion canopy to provide an acceptable heat exchanger, the sides of the canopy being poor in this respect. Also, since the upper surface of the combustion canopy is cooled only by water droplets, the high surface temperature gives rise to the production of steam which necessitates the provision of a large upper heat exchanger to recondense the steam. Furthermore, such a heater cannot be fired without any flow of water droplets otherwise overheating will occur.
Known direct contact water heaters are also disadvantageous in that as the bulk water outlet temperature rises an increasing proportion of the available source heat input is used wastefully to evaporate the bulk water to such an extent that at approximately 89.degree. C. water temperature, all of the available heat is used in evaporating the bulk water. Thus, the water heating efficiency gradually drops off until at this point it becomes zero. This is shown clearly by the curve "A" on the graph of FIG. 3 of the accompanying drawings.
It will be appreciated that in view of the current emphasis being placed on the conservation of energy, there is an urgent need in the field of water heating appliances for a product that improves efficiency.